John Röhl was born in London to a German father and an English mother and grew up bilingual. He did his doctorate in 1965 at Cambridge University and lectured there from 1964 to 1972. He later became Reader and in 1979 Professor of European History at the University of Sussex in Brighton. From 1970 to 1983 he worked on the history commission of the Bavarian Academy of Sciences and Humanities, and was dean at the School of European Studies from 1982 to 1985. Aside from his English professorship, he frequently took on substitute professorial roles in Germany. He was given emeritus status in 1999.
Röhl is considered one of the foremost experts and critics of the WilhelmineGerman Empire under Kaiser William II, in particular following his three-volume biography of the final German Kaiser. In this biography, Röhl developed the theory of William II's 'personal rule', which included ascribing him the main responsibility for the outbreak of the First World War, and levelling strong moral accusations against him (albeit in a strictly scholarly fashion). These theories led to a paradigm shift in German historiography, in which until the 1970s/1980s the Kaiser had been a neglected figure, largely perceived as a 'weak ruler' with little political influence. More recently, however, Röhl's theories have come under increasing criticism, led by the Australian historian Christopher Clark.